Convection and Buoyancy Questions and Answers

Answer: A

A scheme whose entrainment is too weak produces deep convection in air that is far too dry, which contributes to excessive light rainfall and a poor representation of the intraseasonal variability. Increasing the entrainment sensitivity has improved the simulation of the Madden-Julian Oscillation in several models. It is a good example of a small physical detail with large consequences for the simulated climate.

Answer: C

The anvil is usually located at the tropopause.

A cumulonimbus is driven by a strong updraft of buoyant air. At the tropopause the temperature stops falling with height and starts rising in the stratosphere above. The rising air is no longer warmer than its surroundings, so it loses its buoyancy and spreads out sideways, forming the flat, wide anvil top.

The surface layer and the boundary layer are only the lowest tens of metres to a couple of kilometres, near the base of such a cloud. The stratopause, at about 50 km, lies far above the reach of any convective cloud.

Answer: A

Convection is the vertical movement of warmer air upward and cooler air downward.

Air heated at the ground is less dense than its surroundings and rises buoyantly; to replace it, cooler, denser air sinks. The overturning carries heat upward and builds cumulus clouds.

Cooler air rising and warmer air sinking runs against buoyancy and would happen only if forced. Options C and D each describe only half of the exchange, and in the wrong sense.